A respirator is a device designed to protect the wearer from inhaling harmful dusts, fumes, vapors, or gases. Respirators come in a wide range of types and sizes used by the military, private industry, and the public. All respirators have some type of facepiece or mask body held to the wearer's head with straps, a cloth harness, or some other method. The mask body of the respirator covers either the entire face (“Full Face Masks”) or the bottom half of the face including the nose and mouth (“Half-Masks”).
Half-face mask assemblies generally include an exhalation valve that opens in response to increased pressure when the wearer exhales to allow the exhaled air to be rapidly purged from the mask interior. The inhaled (contaminated) air flows through a filter element that is generally placed over inhalation ports to purify the air that is inhaled These inhalation ports also are generally fitted with a one-way valve that closes when the user exhales in order to preserve the filters from degradation by moisture exhaled in the wearer's breath and to direct all the exhalation air through the exhalation valve or diaphragm. It is desirable that the air path between the exhalation valve and the environment be free from blockage or impediments.